1. Field of the Invention
The present invention relates to a range finder system and particularly to a range finder system to detect the distance from an object by irradiating radiation toward an object distance to which is to be detected, based on the principle of base line range finder, and receiving the reflected radiation being reflected by said object.
2. Description of the Prior Art
Heretofore, various kinds of base line range finders have been known without especially showing them here. Particularly, such base line range finders of an upper and lower images matching type or of double images matching type as being so made as conducting automatic range detection by photoelectrically detecting the matching state of the images are known already by Japanese Patent Application Publication Nos. Sho 39-20056 or Sho 41-16225, etc. Further, an automatic focus adjusting device of a camera based on the principle of said base line range finder of images matching type is already known by Japanese Patent Application Publication No. Sho 48-5733, etc.
For example, the Japanese Patent Application Publication No. Sho 39-20056 discloses a base line range finder of automatic upper and lower images matching type which is so made that two photoelectric conversion elements are placed closely to each other at the imaging plane of upper and lower images sandwitching the image dividing line and the matching state of the images is automatically detected without eye sight by said two photoelectric conversion elements in range finding so that the distance to an object can be detected.
Also, the Japanese Patent Publication No. Sho 41-16225 discloses an images matching detection device suitable to a base line range finder of double images matching type which is so made that a photoelectric conversion element is positioned at a focal plane where double images appear, and detection of matching double images can be automatically done by utilizing the fact that the output of said element reaches its maximum value as the double images properly match on said element.
Furthermore, the Japanese Patent Application Publication No. Sho 48-5733 discloses an automatic focus adjustment device of a camera which is so made that utilizing the fact that discrepancy in the two images generated by optical positioning of a base line range finder is a function of the distance to an object, and said function is made as an output depending on the difference of the resistance values in a pair of photoelectric conversion elements, on the other hand, a device generating electric output depending on the proceeding and retreating thereof is provided at a photographing lens, and the output at the photographing lens side follows the output derived from the discrepancy of the above mentioned two images so that the automatic focus adjustment of photographing lens can be done.
However, each of said devices has such common shortcomings that detection of distance is impossible when an object to be sensed does not have distinct difference in the brightness against the surrounding scene, or when it is in a dark place. This is derived from the fact that each of said devices is a so-called a passive type device that is to detect the light generated from the object to be sensed itself (that is the light generated from an object to be sensed or external light reflected by the object to be sensed.)
As a method for eliminating such shortcomings, for example, a so-called active type method has been considered effective that is an artificial radiation is projected toward an object to be sensed and said radiation being reflected by the object to be sensed is detected for conducting distance sensing, and a device employing such method has already been proposed, for example, by U.S. Pat. Nos. 3,435,744 or 3,442,193, etc.
Said U.S. Pat. Nos. 3,435,744 and 3,442,193 are to disclose entirely identical device and these patents disclose an automatic focus adjustment device of a camera which is so made that the ray of light omitted by a light source positioned in a predetermined relationship against a camera is pointed toward an object, and the ray of light reflected by an object is received by a photo-responsive device containing a photoelectric conversion element being positioned in a lateral direction from the light source through a prescribed base line distance, and then said photo-responsive device is brought to matched state against the reflected ray of light, thereby detecting the angle between the ray of light emitted and the ray of light reflected so that focus adjustment of a photographing lens system is done based on thus detected angle.
However, in said method the difference in intensity of weak radiation reflected by an object needs to be detected by a photoelectric conversion element, therefore, for obtaining clear output signal the intensity of radiation by the radiation flux incident into a photoelectric conversion element must be substantially higher than the marginal intensity of radiation which can be detected, thus it has such shortcoming that the accuracy in range detection is lowered as the distance to an object to be sensed becomes greater. Thus, in a device employing above mentioned method the radiation source needs to have high radiation output power, hence power consumption increases and it is not necessarily suitable as a range finder device for use in a small size optical device such as a camera.